When you feel like your body has failed you, maybe you should consider the notion that it might really be the other way around. In what way have we failed our knees? It mostly comes down to chairs and shoes, both of which make it impossible to move correctly.
Pain caused by movement in any joint means that joint is likely doing more work than it should. Why is it overworked? Because the muscles supporting the neighboring joints aren’t pulling their weight. Shoes inhibit movement of the foot to the detriment of the ankle and knee joints, while chairs inhibit the hip joint to the detriment of the knee and lumbar spine.
Let's talk about ankle mobility. A lever needs to rotate around the fulcrum and if there isn’t enough movement at the axis to accomplish this, then you'll have to compensate by moving differently.
The image below shows a goal for ankle range-of-motion. The plantar-flexed ankle is how the foot should look right before the "toe off" moment in the gait cycle. The axis of the ankle and the pulley system of the posterior leg muscles require a straight foot to generate the most force without friction.
Then there are the mechanics of the foot itself. Too often in a shoe-wearing population, the foot is no longer supple enough to conform to the ground, but stiff and chronically everted when bearing weight. This forces the subtalar joint (located below the ankle) to wobble side to side while walking.
Most people's feet are about as supple as a couple loaves of stale ciabatta. That thought kept popping into my head. When I looked it up, I found that ciabatta literally translates to "slipper" bread.
Unyielding feet have been around for a long time. So long, in fact, that as a species we've collectively forgotten how a foot was designed to look and move. Whether you are young or old, an athlete or a couch potato, a fashionista or wish every day was Pajama Friday, your feet likely have much in common with your fellow man. Namely, soreness, bunions, hammer toes, plantar fasciitis, bone spurs, flat arches, arthritis, neuropathy or all of the above. Worst of all, the solution is so simple: First, stop abusing those tired ole dogs and align them so that they can do their job properly; Second, require them to move. ALOT. In novel ways.